The present invention relates to a polymer dispersion comprising an aqueous, continuous phase and dispersed particles of polyurethane and a copolymer or terpolymer produced by emulsion polymerisation of vinyl- and/or acrylic and/or methacrylic monomeric material(s) in the form of multiphase particles. Products of this type are useful as adhesive materials for various types of substrates.
Products of this type are already known in the art e.g. from:
U.S. Pat. No. 3,705,164 (Honig et al assigned to Bayer) discloses the production of aqueous dispersions by polymerizing olefinically unsaturated monomers by free radical polymerization in the presence of a polyurethane emulsion. Sixteen suitable classes of unsaturated monomers are described including vinyl esters, alkyl esters of α,β-unsaturated carboxylic acids as e.g. acrylates and methacrylates and nitrites of α,β-unsaturated carboxylic acids as e.g. acrylonitrile and methacrylonitrile. No preference for any specific monomers is stated. Many of the unsaturated monomeric materials specifically polymerized comprise halogen or sulphur atoms, and/or a high amount of acrylonitrile as it is the intention to use the eventual compositions with pigments as coating compositions. These compositions with a low glass transition temperatures (Tg) of say below −30° C. Such compositions with a (Tg) below −30° C. are unsuitable for structural adhesives as they would be too soft and give too much blocking.
U.S. Pat. No. 4,198,330 (Samuel Kaizerman et al assigned to America Cyanamid) also discloses products obtained by polymerising unsaturated monomers in the presence of a polyurethane latex. Usually high amounts of acrylonitrile (40%) were employed. The unsaturated monomers employed are all monomers which would yield homopolymers with a Tg higher than 60° C., most of those listed have a Tg higher than 80° C. The examples using acrylonitrile use a high level thereof and the polymers produced have Tg of approximately 100° C. A wide variety of organic diisocyanates, including aromatic diisocyanates are listed and the one illustrated in the example is toluene diisocyanate. The objective is to provide films and coatings of improved strength and less surface tack than unmodified polyurethane films and there is no disclosure of their use as adhesive. In fact for use as an adhesive, a certain level of surface tack would be required.
U.S. Pat. No. 5,594,065 (Chao-Fong Tien assigned to Air Products) disclosing certain very low molecular weight polyurethane/hydroxy acrylate hybrid polymers having a M.W. of e.g. 4000, which requires special steps to be taken during the polymerization as e.g. that a chain terminator like dialkanolamide is used for limiting the molecular weight (M.W.) of the polyurethane, sometimes in combination with a chain transfer agent like a thiol for limiting the molecular weight of the acrylic component. The diisocyanates disclosed include also aromatic ones and the two component polyurethane/hydroxy acrylate hybrid polymers obtained are stated to be useful as coating compositions having a good gloss.
U.S. Pat. No. 5,539,018 (Erhard Lühmann et al assigned to Wolff Walsrode) discloses polymer dispersions containing a water-soluble urethane modified allyl ether polyester and polymerised unsaturated monomers as a multiphase product. Although acrylonitrile and methacrylonitrile have been mentioned as a possible ingredient in the lacquers disclosed there is no disclosure that relatively small amounts thereof have a beneficial effect in adhesive compositions.
EP-B-0 309 113 (ICI Americas) discloses that polymer dispersions containing a polyurethane based on 2,4′-diphenylmethane diisocyanate (an aromatic diisocyanate) and a vinyl polymer have superior properties as to hardness and resistance towards water which are important properties in the case of a coating on steel. Acrylonitrile has been mentioned but there is no disclosure it has any beneficial effect in the case of adhesives. The other diisocyanate specifically claimed i.e. toluene diisocyanate is an aromatic diisocyanate.
U.S. Pat. No. 6,063,861 (Christoph Irle assigned to Bayer AG) discloses aqueous polyurethane-polyacrylate dispersions comprising: A) 10 to 95 wt. % based on the total resin solids of a polyurethane dispersion; B) 5 to 90 wt. % based on the total resin solids of a polymer prepared in the presence of component A) from a mixture of vinyl monomers containing 0.5 to 20 wt % based on the total resin solids of the hybrid dispersion of a vinyl monomer containing acetoacetoxy groups and C) an at least difunctional primary or secondary amine having a number average molecular weight of less than 1.000, which is present in an equivalent ratio of amino groups to acetoacetoxy groups of 0.5:1 to 1.1 to 1 in which the wt. % of A) and B) add up to 100. These compositions comprise a diamine as crosslinker and serve as a 1-component coating composition or binder.
EP-A-0 933 412 (Nat. Starch Chem. Invest) discloses water-resistant adhesives comprising an aqueous emulsion polymer which comprises reacting: A) from 80 to 99 wt. % based on the total of monomers of vinyl acetate; B) from 1 to 10 wt. % based on the total of monomers of an N-methylol containing containing copolymerizable monomer wherein the polymerization is conducted in the presence of C) at least 2 wt. % based on the total weight of the aqueous emulsion of polyvinyl alcohol wherein at least 85% of the polyvinyl alcohol is hydrolyzed and D) from 0.1 to 8.0 per hundred parts of monomer in the emulsion of a water-dispersible nonionic polyurethane obtained by reacting an organic polyisocyanate with certain water-soluble polyalkylene glycols and polyhydric branched alcohols. These adhesives comprise water-soluble polyurethanes, not water dispersed particles, of polyurethanes, and hydrolyzed polyvinyl alcohol.
EP-A-0 705 855 (Air Prod & Chem.) discloses a water-based polymeric dispersion comprising a first aqueous dispersion containing a polymer having a plurality of activated keto methylene groups and an effective amount aromatic aldimine containing curing agent which comprises a blend of: said first aqueous dispersion containing said polymer having activated keto methylene groups and a second aqueous dispersion containing a polymer having a plurality of araldimine functionality. The second dispersion that is used to crosslink with the acetoacetate functionality is the important feature of these compositions. The water-based polymeric composition is a blend of two components that can be dispersed separately, then mixed, dispersed together, or one can be dispersed in the other. The compositions are useful for coatings and adhesives.
Many of the compositions described above have environmental disadvantages because they contain e.g. halogen atoms, sulphur atoms and/or volatile organic solvents like acetone, methyl ethylketone, N-methylpyrrolidone, toluene etc. (cf. EP 0 309 113 p. 5 lines 16-23) and the use of such solvents should therefore rather to be avoided.